Re: master 7362554: Widen around c-font-lock-fontify-region. This fixes bug #38049.

[Dmitry Gutov <dgutov@yandex.ru>]

On 14.11.2019 16:29, Eli Zaretskii wrote:
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> Date: Thu, 14 Nov 2019 16:05:13 +0200
>> Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
>>
>> The hope is that calling vertical-motion (or font-lock-ensure directly)
>> inside narrowing is a rare occasion
> 
> Why do we need to have such hopes?

For starters, because it's the current expectation of mmm-mode. :-)

That's selfish, I know. But the counter-examples are sufficiently rare.

> The reality could be different,
> and I'd like us to support those different conditions.  It doesn't
> sound like it's much harder.

There are options, sure. But I think all of them will require explicit 
support from major modes. Like adding a new element to 
prog-indentation-context, which will be a function which either returns 
new narrowing bounds or does the narrowing itself. And then the major 
mode will have to make sure to use it everywhere.

This particular case is annoying because it seems to mean that the 
(widen) call in font-lock-default-fontify-buffer doesn't help, and a lot 
of font-lock-keywords matchers will need to call (widen) anyway.